It is well known in the art that the electrical properties of conductive polymers frequently depend upon their temperature. A very small proportion of conductive polymers exhibit a positive temperature coefficient (PTC), i.e., rapid increase in resistivity at a particular temperature or over a particular temperature range. Materials exhibiting PTC behavior are useful in a number of applications in which the size of the current passing through a circuit is controlled by the temperature of a PTC element forming part of the circuit.
PTC circuits are typically used as self-thermostating circuits such as in mirror heaters and seat heaters found in automobiles and the like. They are used in place of an external thermostat. Although they have been used for years in these types of applications, the PTC circuits typically have problems such as resistance shift stability, powered on/off cycling inconsistency, and sensitivity to the adhesive used in the fabrication. All these issues can and do have a negative impact on a functional PTC circuit. It is the purpose of this invention to help alleviate these issues and thus help produce a more efficient and reliable PTC circuit.